In connection with high-speed data transfer between devices, a demand for high-speed long-distance transfer has lately been mounting. In the case of the high-speed data transfer, there is an increase in transmission loss in a transmission line, and a decrease in received amplitude becomes pronounced. In addition, there will be a pronounced decrease in eye aperture margin due to the effect of inter-symbol interference. Techniques such as pre-emphasis, de-emphasis, and decision feedback are well known as means for solving this problem.
The inter-symbol interference refers to a phenomenon wherein adjacent symbols interfere with each other, thereby causing a waveform to be distorted. The eye aperture margin refers to an aperture width of an eye pattern (eye diagram) in the direction of time base, which is a waveform expression obtained by synchronizing time responses of a signal waveform, with each other, for every basic period before being superimposed one another.
The pre-emphasis, or the de-emphasis is carried out by the action of a feed forward equalizer (FFE) within an integrated circuit on a transmission side. At the time of the pre-emphasis, amplitude of a first bit, in the vicinity of a threshold where a level undergoes transition, is increased. On the other hand, at the time of the de-emphasis, amplitudes of a second bit, and thereafter are decreased.
Further, the decision feedback is carried out by the action of a decision feedback equalizer (DFE) within an integrated circuit on a receiving side. At the time of the decision feedback, data determination of received amplitude that has decreased due to attenuation after passing through a transmission line is determined on by use of a determination result of “1” or “0” once determined against a readout signal, thereby removing inter-symbol interference
In JP-A-Hei11(1999)-205394, there is shown a receiving circuit as one example of decision feedback equalizer, for determining which of binary a received digital signal represents, thereby outputting a determination value. More specifically, a value determined previous time is held in a flip-flop, and a result obtained by comparing either of threshold values differing from each other with a received signal according to a held value is outputted as the determination value.